FCC catalysts used today in cracking process for heavy oils are among the most sophisticated catalysts, having high selectivity towards gasoline range products due to the presence of large pore faujasite type zeolite in various compositions. Increasing cost of crude is forcing refineries to process opportunity feeds having high carbon residue, nitrogen, aromatics and contaminants such as nickel and vanadium for maintaining decent returns on investment. Of all the contaminants present in feeds, metal contaminants pose the greatest challenge, as some of them permanently cripple the catalytic activity. Nickel and vanadium are the most prominent among all the metals requiring remedy for their undesired properties. Nickel is well known for dehydrogenation of feed and products under normal FCC operation conditions thereby producing higher coke and dry gas. These effects are predominant with catalysts having higher surface area. Vanadium, unlike nickel, is known for zeolite destroying property and for even worse effects by hopping from aged catalyst particle to fresh catalyst particle while carrying out the destructive action. Vanadium pentoxide, formed during severe regeneration operation, gets converted to vanadic acid which reacts with structural alumina of zeolite and also with structure supporting rare earth species. Thus, presence of vanadium in the feed can permanently reduce activity of the FCC catalyst. Processing such feeds demand catalysts having higher metal tolerance, and mesoporous active matrix. Formulations designed for processing of heavy feeds are known as Resid Fluid Catalytic Cracking (RFCC) catalyst. Such feeds sourced from streams such as light oil, inter oil, heavy oil, deashphalted oil, short residue, heavy gas oil, coker gasoil having nickel and vanadium in the respective range 2-50 ppm and 5-120 ppm enrich the catalyst with total metals from 1-3 wt %. As discussed earlier, presence of vanadium metal on catalyst will permanently destroy catalytic activity while nickel contributes towards higher dry gas along with coke. In order to maintain good activity, catalyst make-up rate is higher while processing metal rich feeds.
For taking care of higher metals while processing metal laden feeds, catalyst manufacturers employ higher concentration of hydrothermally stable REUSY zeolite in range 40-50 wt % along with inbuilt metal passivator component bonded by customized mesoporous matrix. Such catalysts suffer from flexibility in usage, as processing of lighter feeds does not need complex compositions and high value ingredients. Even, if softer normal FCC catalysts are added to top-up, major chunk is still a low active RFCC catalyst.
Several types of additives were introduced in late eighties to overcome limitations in conventional FCC/RFCC as wholesome catalysts. Such additives offered flexibility of addition and termination whenever special effects are desired. Metal passivator is one of such additives. Following are some of most prominent prior art formulations/products which were claimed to be effective for passivation of nickel and vanadium.
U.S. Pat. No. 3,930,987 describe zeolite containing cracking catalysts, which are impregnated with a solution of rare earth salts on matrix. This particular process was developed with an intention of enhancing of efficacy of zeolite in catalytic activity.
For overcoming destructive properties of vanadium and coke forming tendencies of nickel in FCC catalysts, several passivation solutions were discussed in U.S. Pat. Nos. 4,111,845, 4,153,536 and U.S. Pat. No. 4,257,919, which were based on antimony, indium or bismuth.
U.S. Pat. No. 4,515,683 discloses a method for passivating vanadium on catalytic cracking catalysts wherein lanthanum is nonionically precipitated on the catalyst prior to ordinary use; however the refiner has no control on content of metal passivator component as it is an integral part of the main cracking catalyst.
Besides solid metal passivators, there are a number of disclosures on applications of liquid metal passivators. U.S. Pat. No. 4,562,167 refer to liquid metal passivator solution containing Sb and Sn compounds.
U.S. Pat. No. 4,929,583 refers to a process for the catalytic cracking of a vanadium-containing hydrocarbon charge stock by contacting the feed with a catalyst having a weak anion component selected from SrCO.sub.3, SrTiO.sub.3, BaCO.sub.3, Ce.sub.2(CO.sub.3)3 etc.
U.S. Pat. No. 4,938,863 describes a process for making a metal tolerant catalyst with a zeolite in an alumina-free binder or coating, preferably silica, with a vanadium getter additive.
U.S. Pat. No. 5,057,205 refers to a process with an additive for catalytic cracking of high metal content feeds including residues. The catalyst additive comprises of an alkaline earth metal oxide and an alkaline earth metal spinel, preferably a magnesium aluminate spinel.
U.S. Pat. No. 5,071,806 discloses a composition for the catalytic cracking of feeds with high metals, the catalyst comprising a magnesium-containing clay material, a silica-alumina cogel, and zeolite.
U.S. Pat. No. 5,173,174 describes a catalyst matrix comprising bastnaesite and a limited quantity of a large pore boehmite alumina for reducing harmful effects of nickel and vanadium on catalyst activity and selectivity.
U.S. Pat. No. 5,304,299 discloses a catalytic cracking catalyst combined with a rare earth, preferably lanthanum-containing catalyst/additive to enhance the cracking activity and selectivity in the presence of nickel and vanadium (Ni and V). The preferred additives comprise of lanthanum, neodymium oxide and/or oxychloride dispersed in a clay/alumina matrix, wherein the alumina is derived from an aluminum hydroxychloride sol. It may be noted that application of aluminum hydroxychloride as binder containing about 17-wt % chlorine, needs additional process while manufacturing such binder-based additive.
U.S. Pat. No. 5,384,041 discloses a vanadium trap for use in FCC which comprises a major amount of calcined kaolin clay, free magnesium oxide and an in-situ formed magnesium silicate cement binder.
U.S. Pat. Nos. 5,520,797 and 4,359,379 describe processes for the fluid catalytic cracking of heavy oils rich in Ni and V by withdrawing a portion of ferrite-containing catalyst particles circulating in a fluid catalytic cracking apparatus, by using a magnetic separator.
U.S. Pat. No. 5,603,823 discloses an additive composition containing Mg—Al oxide spinel with lanthanum and neodymium oxides.
U.S. Pat. No. 5,965,474 describes a catalytic composition for passivating metal contaminants in catalytic cracking of hydrocarbons with ultra-large pore crystalline material as an additive or catalyst composition. The metal passivator is incorporated within the pores of the large pore crystalline material. In a preferred embodiment, the metal passivator is a rare earth metal compound or an alkaline earth metal compound.
U.S. Pat. No. 5,993,645 disclose phosphorus treated cracking catalyst containing soda and phosphate with high tolerance to contaminant metals.
US 20070209969 provides a catalyst and a process for cracking heavy feedstocks employing a catalyst with one or more zeolites having controlled silica to alumina ratio.
U.S. Pat. No. 6,673,235 disclose a fluid catalytic cracking catalyst with transitional alumina phase formed within the microspheres to crack resid or resid-containing feeds.
U.S. Pat. No. 6,723,228 disclose an additive in the form of a solution, colloid, emulsion or suspension containing antimony, bismuth and combination of these.
EP0350280, disclose metals tolerant FCC catalyst system comprising an admixture of a LZ-210 type molecular sieve component and a bastnaesite type rare earth component dispersed in a large pore matrix containing substantial amounts of a large pore, low surface area alumina. This invention refers to a catalyst and process in which zeolite content is ranged from 10-50 wt % and rare earth component is present from 0.5-25-wt %. Referred formulation is a wholesome cracking catalyst having very high cracking functional zeolite component in range 10-50 wt %, which produces significant amount of catalytic coke.
From the various prior art processes and formulations for metal passivation in FCC process, it can be seen that rare earth based compounds have been used to mitigate the deleterious effects of metals especially that of vanadium and reduce the coke making tendencies of both nickel and vanadium for minimizing deleterious effects of vanadium contaminant vide using them as an integral part of FCC catalysts as can be seen in EP 0350280 and U.S. Pat. No. 4,515,683 and as rare earth based additive as disclosed in patents U.S. Pat. No. 5,304,299. The disadvantages on employing RFCC catalysts with inbuilt metal passivation components is the inflexibility to have metal passivation in the process as and when required while processing of feeds rich in metals. As the main unit catalyst inventory is large, dilution effects due to E-cat can be seen, even when the feed contains lesser amount of metal.
These disadvantages have been reported with the application of prior art additive. However, additives too suffer from dilution of main cracking catalyst. Higher the level of metals in the feed, higher the addition rate for metal passivation additive. As a result, employing additives beyond certain limits dilutes main host catalyst, thus lowering of conversion. Thus, there is a need for the development of an effective metal passivator additive, which can effectively passivate the metals and minimize the effect of dilution.